The PHP class files (suffix .inc) and the templates (suffix .ihtml)
are installed to a location where PHP engine can find them. This
location is specified in the PHP
engine init file (usually /usr/local/lib/php.ini),
using the include_dir directive. This
must be a separate secure location so that they are not served
directly out in response to browser HTTP requests.

One of the files includes subclass declarations of the PHPlib
classes such as Session and Auth to specify your own database setup
details. The tracepack generic classes, the form handler classes and
the user interaction handler classes are installed in the same
secure location.

The templates (suffix .ihtml) your subclass of PHPlib's
Form uses
can as well be installed in a separate directory dedicated to template
storing, but the location must be present in the PHP engine init file
include_dir directive.